1. Field
The present invention relates generally to data communication, and more specifically to techniques for performing beam-steering and beam-forming for wideband MIMO/MISO systems.
2. Background
A multiple-input multiple-output (MIMO) communication system employs multiple (NT) transmit antennas and multiple (NR) receive antennas for data transmission. A MIMO channel formed by the NT transmit and NR receive antennas may be decomposed into NS independent channels, with NS≦min{NT,NR}. Each of the NS independent channels is also referred to as a spatial subchannel or eigenmode of the MIMO channel.
A multiple-input single-output (MISO) communication system employs multiple (NT) transmit antennas and a single receive antenna for data transmission. A MISO channel formed by the NT transmit and single receive antenna includes a single spatial subchannel or eigenmode. However, the multiple transmit antennas may be used to provide transmit diversity or to perform beam-forming or beam-steering for the data transmission.
For a wideband system, orthogonal frequency division multiplexing (OFDM) may be used to effectively partition the overall system bandwidth into a number of (NF) orthogonal subbands, which are also referred to as frequency bins or subchannels. With OFDM, each subband is associated with a respective subcarrier upon which data may be modulated. For a MIMO/MISO system that utilizes OFDM (i.e., a MIMO/MISO-OFDM system), each subband of each spatial subchannel may be viewed as an independent transmission channel.
The spatial subchannel(s) of a wideband MIMO/MISO system may encounter different channel conditions due to various factors such as fading and multipath. Each spatial subchannel may experience frequency selective fading, which is characterized by different channel gains at different frequencies of the overall system bandwidth. This may then result in different signal-to-noise ratios (SNRs) at different frequencies of each spatial subchannel. Moreover, the channel conditions may deteriorate to a level where most of the spatial subchannels are highly degraded. In these situations, improved performance may be achieved by using only the best spatial subchannel for data transmission.
There is therefore a need in the art for techniques to process data for transmission on a single spatial subchannel when warranted by the channel conditions.